I found marriage record of an Elizabeth Sneddon to a John Reid, Polmont, Scotland, 1841, BUT !!!
... on the LDS Family History search of the births of Margaret/Robert/Andrew their Mother is NOT Elizabeth Sneddon, but Margaret SIM ?????

Elizabeth Reid (without husband) arrived with her 3 children at the Port of New York in 1848, disappeared until 1859, found re-married to a John Baird, living in Pennsylvania.